1. Field of the Invention
The present invention relates to temperature detectors utilizing nuclear quadrupole resonance, nuclear magnetic resonance or like resonance-absorption phenomena.
2. Description of the Prior Art
The nuclear quadrupole resonance-absorption frequency of certain substances is known to depend upon temperature. Such substances include for example the Cl.sup.35 isotope of Cl in chlorate compounds such as KCl0.sub.3 or NaCl0.sub.3. Also, there is temperature dependence of the nuclear magnetic resonance-absorption frequency of the Cr.sup.53 isotope of Cr in a ferromagnetic compound such as CrBr.sub.3, and of an antiferromagnetic substance such as MnF.sub.2 or CrC1.sub.3. Temperature detectors or thermometers based on such temperature-dependence have been proposed. The present invention relates to improvements in such thermometers.
There have been many studies made of this type of thermometer. One study by G. B. Benedek and T. Kushida entitled "Precise Nuclear Resonace Thermometers", appeared in The Review of Scientific Instruments, Vol. 28, No. 2, pp. 92-95, Feb. 1957. Another study by J. Vanier entitled "Nuclear Quadrupole Resonance Thermometry", appeared in Metrologia, Vol. 1, No. 4, pp. 135-140, Oct. 1965. A number of topics of the resonance thermometer have been discussed by J. Vanier in "Nuclear Magnetic Resonance Thermometry", Temperature -- Its Measurement and Control in Science and Industry, Vol. 4, Part 2, pp. 1197-1212, ISA, Pittsburgh, Penna., 1972. U.S. Pat. 3,373,348, to J. Vanier, shows details of one type of thermometer based on such concepts.
Despite this extensive work, prior art techniques have not been capable of providing a practical resonance thermometer as yet. This is chiefly because the absorption signal available is too weak and the absorption frequency too narrow in width, characteristics inherent in the prior art thermometry. This has necessitated the use of highly skilled operators to maintain thermometer functions, and has limited its range of utility.